Nutrients 2015, 7, 6195-6212; doi:10.3390/nu7085276 OPEN ACCESS nutrients ISSN 2072-6643 www.mdpi.com/journal/nutrients Article Is It the Appropriate Time to Stop Applying Selenium Enriched Salt in Kashin-Beck Disease Areas in China? Yujie Ning :, Xi Wang :, Sen Wang, Feng Zhang, Lianhe Zhang, Yanxia Lei and Xiong Guo * School of Public Health, Health Science Center, Xi’an Jiaotong University, Key Laboratory of Trace Elements and Endemic Diseases, National Health and Family Planning Commission, Xi’an, Shaanxi 710061, China; E-Mails: [email protected] (Y.N.); [email protected] (X.W.); [email protected] (S.W.); [email protected] (F.Z.); [email protected] (L.Z.); [email protected] (Y.L.) : These authors contributed equally to this work. * Author to whom correspondence should be addressed; E-Mail: [email protected]; Tel.: +86-029-82655091; Fax: +86-029-82655032. Received: 5 June 2015 / Accepted: 20 July 2015 / Published: 28 July 2015 Abstract: We aimed to identify significant factors of selenium (Se) nutrition of children in Kashin-Beck disease (KBD) endemic areas and non-KBD area in Shaanxi Province for providing evidence of whether it is the time to stop applying Se-enriched salt in KBD areas. A cross-sectional study contained 368 stratified randomly selected children aged 4–14 years was conducted with 24-h retrospective questionnaire based on a pre-investigation. Food and hair samples were collected and had Se contents determined with hydride generation atomic fluorescence spectrometry. Average hair Se content of 349.0 ˘ 60.2 ng/g in KBD-endemic counties was significantly lower than 374.1 ˘ 47.0 ng/g in non-KBD counties. It was significantly higher in the male children (365.2 ˘ 52.3 ng/g) than in the female (345.0 ˘ 62.2 ng/g, p = 0.002) and significantly higher in the 4.0–6.9 years group (375.2 ˘ 58.9 ng/g) than the 7.0–14.0 years group (347.0 ˘ 56.1 ng/g, p < 0.01). Gender, living area, Se intake without supplements, Se-enriched salt, oil source and protein intake were identified as significant factors of hair Se contents. Cereals, meat and milk were commonly included as significant food categories that mainly contributed to Se intake without supplement of the whole population. Balanced dietary structure without Se supplement could effectively enhance and maintain children’s Se nutrition. It may be the time to stop applying Se-enriched salt in KBD areas in Shaanxi Province. Nutrients 2015, 7 6196 Keywords: selenium; Kashin-Beck disease; selenium content; factor; food item 1. Introduction Until 1957, scientists have discovered the essential positive effects of Se on animals breaking the limitation of only studying its biologically toxic effects [1,2]. Since then, disorders related to Se-deficiency have been revealed in human beings, mice and other mammalian animals such as pigs and horses [3–9]. Kashin-Beck disease (KBD) is a serious kind of endemically deformed osteoarthropathy with unclear etiology and pathology. It mainly is distributed from the northeast to southwest China, where the environment is Se-deficient [10]. For decades of research, Se deficiency was found to be one of the main risk factors of KBD [11,12]. As KBD attacks local residents in childhood and clinically manifests [13] in adulthood, effective prevention is the key to protect the health of children as always. Because of Se deficiency being considered a risk factor of KBD, various approaches of supplementation [14], especially Se-enriched salt (sodium selenite: table salt = 1:60,000) [15,16], which is the most economical way for low-income families, had been continuously done in endemic areas. The Se enriched salt turned out to be effective to decrease the incidence of KBD and alleviate the symptoms [11,17]. However, it was suggested to cease the supplement in Shaanxi Province because there are rare new patients in endemic areas without supplements in recent years. But as far as we know, there is no reasonable evidence to support this suggestion. Nonetheless, apart from Se-enriched salt, some other dietary and/or non-dietary factors may also play positive roles in controlling KBD, according to our recent findings that are based on an analysis of a three-year cohort study [18]. To provide proper evidence for whether it is the time to stop Se supplements in the KBD area in Shaanxi Province, we conducted a sectional investigation based on a prior study to identify which factors are associated with the Se nutrition status in children, in another words, contributing to the controlling of KBD. 2. Experimental Section 2.1. Study Design and Subjects According to the results of prior investigation, we adjusted the contents of questionnaires, most of which were about the food items, such as deleting the unusual foods and adding the ones that the residents often consume. Then, we conducted a 2:1:1 matched cross-sectional investigation in the same counties in Shaanxi Province where the prior investigation was performed from June to September in 2012 and 2013, avoiding summer vacations (study design is shown in Figure1). Nutrients 2015,, 7 61973 Figure 1. This diagram shows the study design including the stratified random sampling Figure 1. This diagram shows the study design including the stratified random sampling process and the contents of the investigation. process and the contents of the investigation. A s stratifiedtratified random sampling method was applied to recruit subjects. According to the design, 2:1:1 matching means that two children in the Se Se-supplemented-supplemented KBD area (Linyou and Bin County) were selectedselected versus one child in in the the non non-supplemented-supplemented KBD KBD area area (Ningshan (Ningshan County, County, internal control) and versus one childchild inin the the non-KBD non-KBD area area (Liquan (Liquan County, County, external external control) control) separately. separately. All theAll subjects the subjects were wereaged aged 4–14 4 years–14 years and Han and nationals,Han national whichs, which eliminated eliminated the interferences the interferences of genetic of genetic background background and racial and racbias.ial Thebias.diagnosis The diagnosis criterion criterion of KBD of KBD [WS/T [WS/T 207-2010] 207-2010] in China in China was was used used to distinguish to distinguish patients patients and andhealthy healthy children. children. Subjects Subjects with anywith other any osteoarthropathyother osteoarthropathy would bewould excluded. be excluded. Based on Based the results on the of resultsthe pre-investigation, of the pre-investigation, sample size sample was calculated size was calculated according according to Equation to (1).Equation (1). 2 2 2 S k ψ α,βpν1,ν2q iS{ /k n “ , ( , ) ∑ i (1) = 2 (1) Xi ´ X 2{ pk ´ 1q α β 1 2ř ∑(X i − X ) /(k −1) 2 ř ` ˘ k is the county number, Si is the sum of variances of hair Se content among groups in k is the county number, S22 is the sum of variances of hair Se content among groups in pre- pre-investigation, Xi ´ ∑X i is the sum of deviation from averages of hair Se contents among 2 ř groups in pre-investigation,− ÎS´ = 0.05, β = 0.10, S2{k = 4258.6, X ´ X { pk ´ 1q = 256.5, investigation, ∑(X i ` X ) is the˘ sum of deviation fromi averages of hair Sei contents among groups in S2{k ř i = 16.6, ν = k´1,ν = 8, k = 4, 2 “2.17, n = 78. 2 X X k 1 1 2 0:05;0:10p3;8q prep-investigationi´ř q{p ´ q , Α = 0.05, β = 0.10, ∑řSi /k = 4258.6, ř∑` (X i − X )˘/(k −1) = 256.5, ř To ensure2 the response rate, 15% more subjects than calculated were required, thus sample size ∑Si /k increased to2 90 per county = 16.6 with, ν1 30= k subjects−1, ν2 = in∞, each k = 4 mild, ψ 0 (KBD.05,0.10(3 prevalence,∞) = 2.17, n < = 15%), 78. medium (15% ¤ KBD − ( − ) prevalence∑(X i X ) </ 30%)k 1 and severe (KBD prevalence ¥ 30%) endemic area which divided according to the primaryTo en prevalence;sure the response meanwhile, rate, 15% an equal more amount subjects of 90than subjects calculated were were required required, in a non-KBDthus sample county. size increasedEventually, to368 90 per eligible county subjects with were30 subjects included. in each mild (KBD prevalence < 15%), medium (15% ≤ KBDAll prevalence the subjects < 30%) and guardians and severe (who (KBD were prevalence responsible ≥ 30%) for the endemic children’s area meals) which were divided informed according and togave the their primary consents prevalence about the; meanwhile, questionnaire an andequal sample amount collection. of 90 subjects The study were was required approved in bya non the- ethnicKBD ccommitteeounty. Eventually, of Xi’an 368 Jiaotong eligible University subjects (No.2015-070, were included. Date: 2 March 2015). Nutrients 2015, 7 6198 2.2. Data Collection 2.2.1. Anthropometric Measurements Height and weight measurements were carried out in children in light clothing and without shoes with traditional scales for medical use (RGZ-120, range 60 cm–200 cm/ 5 Kg–120 Kg with 0.1 cm/0.1 Kg measurement error respectively). All results were recorded by a mean value which calculated from two times of measurements, except for a median which would be used instead if a third measurement was taken when the difference between the former two measurements was more than 10%. Then Children’s BMIs were calculated according to Equation (2). W eight pKgq BMI “ (2) Height2 pm2q 2.2.2. Questionnaire Investigation Semi-quantitative questionnaires with a series of dietary and non-dietary items (briefly presented in Table1) were given to and completed by the subjects and their guardians after instructions explained thoroughly by two research assistants who were well-trained and fluent in the local language.